1. Field of the Invention
The present invention relates to a variable displacement refrigerant compressor adapted for use in an automotive air conditioning system that lacks a clutch between the compressor and the automotive engine. More specifically, the invention relates to a variable displacement compressor of the type that shuts off the flow of refrigerant gas to the suction chamber while the compressor is in its minimum displacement state by using a shutoff member, which is located in a central bore formed in the cylinder block.
2. Description of the Related Art
For better understanding of the problem solved by the invention, a typical variable displacement refrigerant compressor of the same type as that of the present invention will be explained.
The compressor comprises a housing defining therein a crankcase, a suction chamber receiving refrigerant gas before compression and a discharge chamber receiving refrigerant gas after compression. The housing includes a cylinder block having a front end surface exposed to the crankcase and including a plurality of cylinder bores each receiving therein a working piston. The compressor further comprises a drive shaft rotatably supported in the crankcase, a swash plate supported on the drive shaft to rotate therewith and to tilt with respect to the axis of the drive shaft between minimum and maximum tilt angle positions while moving along the drive shaft, thereby making a wobbling movement at a variable tilt angle. Each piston is slidably received in one of the cylinder bores and is operatively connected to the swash plate such that the wobbling movement of the swash plate at the variable tilt angle is converted into reciprocal movement of the pistons, and the stroke of the pistons in the associated cylinder bores varies accordingly. The housing further includes a suction passage receiving an inflow of refrigerant gas from an air conditioning system, to which the compressor is connected. The suction passage is communicable with the suction chamber.
Formed axially through the cylinder block is a central bore aligned with the drive shaft. One end of the bore opens to the crankcase, and the other end opens to the suction passage. The compressor further includes a shutoff means in the form of a cup-shaped spool slidably fitted in the above central bore for shutting off fluid communication between the suction passage and the suction chamber to stop the inflow of refrigerant gas into the cylinder bores when the swash plate is brought to its minimum displacement location. The rear end of the drive shaft is inserted into the shutoff spool and is supported by a radial bearing mounted on the drive shaft within the shutoff spool. The compressor further includes a displacement control valve for controlling the tilt angle of the swash plate in response to a change in the cooling demand or load.
In this type of compressor, the swash plate tilts in response to the difference between the pressure in the crankcase and the pressure in the cylinder bores. When there is no cooling demand, the swash plate is brought to the minimum angle tilt angle position, and the shutoff spool is moved in the central bore to close the suction passage so the flow of refrigerant gas into the suction chamber is shut off. In this state, the refrigerant gas within the compressor is circulated through the discharge chamber, the crankcase, the suction chamber and the cylinder bores and, simultaneously, lubrication oil contained in and entrained by the refrigerant gas lubricates the internal parts of the compressor.
Regarding compressors of this type, however, there has been no disclosure with reference to the arrangement of the radial bearing relative to the central bore of the cylinder block. In compressors of this type having a relatively short cylinder block and hence a short central bore receiving the shutoff spool, it has been feared that the radial bearing may slide to such an extent that the center of that radial bearing, as defined by an imaginary plane extending perpendicularly to the drive shaft axis and passing through the axial midpoint of the bearing, will come out of the central bore, or move beyond the front end surface of the cylinder block, while the swash plate is being moved toward its maximum tilt angle position. If this occurs, the shutoff member would tend to incline within the central bore with respect to the axis of the drive shaft and become misaligned with the axis of the drive shaft. When the shutoff member is subsequently moved rearward while in an inclined state in conjunction with the movement of the swash plate to its minimum tilt angle position in response to a decrease in the cooling demand, the shutoff member may fail to completely shut off the suction passage so that some of the refrigerant gas in the suction passage may flow into the suction chamber. This would result in performance of the cooling operation even when there is no demand for cooling.